This invention relates to air filtration systems using ionized air and, especially, to air cleaning systems using a plurality of point ionization sources in a room environment.
One type of prior art clean air filtration system employs an ionizer to create ions which attach themselves to dust and dirt particles. The charged particles are then collected such as in a filter or an electrostatic precipitator. The efficiency of such a system depends heavily on the effectiveness of the ionizer to create charged particles which can then be collected.
Traditionally, two types of ionizers have been used in clean air filtration systems (room purifiers) to enhance the performance of the filter used to collect dust and dirt particles.
One type of ionizer consists of a plurality of wires and ground plates. When a high voltage is applied to the plurality of wires, the electric field created between the wires and plates breaks down air molecules, creating large numbers of ions. The ions move to the ground plates at very high speed and collide with dust and dirt particles in the air, transferring electrostatic charges to the dust and dirt particles. These wire-plate type of ionizers are usually disposed upstream of a filter system to pre-charge dust and dirt particles for collection in the filter system. While an effective mechanism for charging particles, this type of ionizer is expensive to construct, requires a high operating current, making it expensive to operate, and is a potential safety hazard due to the very high voltages and high currents employed. This type of ionizer is commonly used in controlled air spaces such as furnace and air conditioning ducts.
Another type of ionizer, which is widely used in room air cleaners or purifiers, is a point ionizer. In a point ionizer, a high voltage, but a much lower current than is typically used in a wire-plate type ionizer, is applied to a point electrode or electrodes to create ions. Again, these ions charge particles of dust and dirt and thereby enhance the performance of a filter.
It is typical of these cleaners or purifiers for the point ionizers to be positioned at or near the exit of the air passing through the cleaners or purifiers. Typically, this is done to disperse ionized particles throughout the room. At least some of these ionized particles would then find their way back to the inlet of the cleaners or purifiers and aid in the operation of the cleaners or purifiers.
An example of an exit point ionizer is U.S. Pat. No. 4,376,642, Verity, Portable Air Cleaner Unit, which describes a portable air cleaner unit. An air mover such as a fan is disposed downstream of the main filter, and an exposed negative ion source is disposed downstream of the fan on the external surface of the air outlet. The main filter consists of fibers shredded from a non-carcinogenic plastic membrane which has been permanently electrostatically charged. The negative ion source ionizes the cleaned air as it leaves the cabinet.
Another example of an exit point ionizer is U.S. Pat. No. 5,268,009, Thompson et al, Portable Air Filter System, a portable air filter system for use in the home, offices, or other areas where it is desired to remove airborne particulate matter from the air. The air filter system includes an ionizer for supplying negative ions to the air exiting through the outlet. The ions charge foreign particles in the air. As a result, when the charged foreign particles are drawn into the inlet of the system, the particles are retained on the filter medium.
Still another example of an exit point ionizer U.S. Pat. No. 5,332,425, Huang, Air Purifier, which describes an air purifier having an extended and tapered discharging copper needle is electrically coupled to a high voltage generator contained within the purifier housing and produces negative ions. The discharging needle is pointed in contour and has an apex end located adjacent the air exit opening. The discharging needle extends in the direction of the passage of high pressure air from the purifier housing which allows the discharging needle to vibrate responsive to the high pressure air flow and increases the amount of negative ions mixed with the air passing from the purifier housing.
These exit ionizers are very effective at charging particles, and has much lower cost and little safety hazard. However, point ionizer systems typically are positioned at the air exit of the purifier, i.e., downstream of the filter. With exit air ionizers, charged particles are discharged into room air, and stay in the air for a significant amount of time before being re-circulated through the filter. As a result, a significant number of these charged particles are removed by other external surfaces such as walls, carpets, human bodies and furniture surfaces, instead of the filter.
Other ionizing filtration systems use point source ionizers at or near the air inlet to the filtration system. Typically, these filtration systems are designed to either disperse ions throughout the room, as do exit ionizers, or are designed to inject ions directly into the air stream within the air inlet of the filtration system.
An example of the type of air cleaning apparatus which diffuses ions throughout the room is shown in U.S. Pat. No. 5,980,614, Loreth et al, Air Cleaning Apparatus, which describes an air cleaning apparatus, especially for cleaning of room air. The device includes an ionizing device having a unipolar ion source formed by a corona discharge electrode, an electrostatic precipitator connected to a high-voltage source and having a flow-through passageway for air to be cleaned and two groups of electrode elements of one group being interleaved with and spaced from the electrode elements of the other group and arranged to be a potential different from that of the other group. While the corona discharge electrode is positioned near the air inlet to the apparatus, the corona discharge electrode is arranged such that the ions generated at the electrode can diffuse essentially freely away from the electrode and thereby diffuse substantially freely throughout the room in which the ionizing device is positioned. As such, the apparatus described in Loreth et al suffers from many of the same disadvantages as the exit ionizers discussed above.
Air filtration systems which are designed to inject ions directly into the air stream at or near the air inlet of the air filtration system or with the internal air stream of the filtration system typically do not achieve optimum efficiency in air cleaning. Typically, in these systems the number of ions generated and the ability of the ions generated to attach to particles of dust and dirt are limited both by the proximity of the ion generation source to the ion collector and by the limited length of time in which the ions have to attach to particles of dust and dirt in the air flow stream within the filtration system.
Thus, while many prior art systems exist which utilize ion generators, and which utilize point source ionizers, such prior art systems suffer numerous disadvantages as discussed above.
Some prior art air filtration systems utilize a centrifugal fan to move air through the filtration system. While such fans are efficient and are operational over a wide range of pressure drops, centrifugal fans are relatively noisy. As such, centrifugal fans suffer significant disadvantages for use in portable, room air filtration systems. Axial fans are considerably less noisy, deliver a uniform straight airflow and can be made very small but are very sensitive to pressure drops as such their use in filtration systems is limited.
In its several embodiments, the present invention overcomes many of the disadvantages of prior art air filtration systems. The air filtration system of the present invention achieves a significant improvement in operational efficiency without significantly suffering the disadvantages of contaminating an entire room with charged ions and thereby causing a significant amount of dust and dirt particles to accumulate elsewhere on surfaces within the room such as walls, furniture and even people. In some embodiments, the combination of a channel filter particulate collection surface and an axial fan allows the filtration system to operate with less noise and less power facilitating an ability to operate continually without attendant lowered air flow due to particulate build-up in conventional filter media, with or without ionization as a portable room air filtration system.
In a preferred embodiment, a plurality of point ionization sources are positioned in the proximity of the periphery of the air flow channel and being oriented to generate ions in the proximity of the air flow channel in a direction generally upstream from each respective one of the plurality of point ionization sources. A particulate collection surface is positioned within the air flow channel in a downstream direction from the plurality of point ionization sources. The particulate collection surface is electrostatically charged in an opposite direction with respect to ground than the electrical charge of the ions.
In another embodiment, a plurality of point ionization sources are positioned in the proximity of the periphery of the air flow channel and being oriented to generate ions in the proximity of the air flow channel in a direction generally upstream from each respective one of the plurality of point ionization sources. A particulate collection surface is positioned within the air flow channel in a downstream direction from the plurality of point ionization sources. The particulate collection surface is electrostatically charged in an opposite direction with respect to ground than the electrical charge of the ions. An ion trap is positioned within the air flow channel between the plurality of ionization sources and the particulate collection surface. The ion trap is relatively electrically neutral as compared with the particulate collection surface and the ions.
In a preferred embodiment, the major longitudinal axis of the ionization head is oriented in an orientation angle with respect to the upstream to downstream direction and wherein the orientation angle is not more than sixty degrees inward toward the air flow channel and not more than ninety degrees outward away from the air flow channel.
In a preferred embodiment, the filtration system of the present invention also comprises a plurality of flow channels, one of each of the plurality of flow channels at least partially surrounding at least a portion of each respective one of the plurality of point ionization sources.
In a preferred embodiment, a portion of the air flow which is downstream of the particulate collection surface is directed past the ionization head in a direction generally opposite to the upstream to downstream direction.
In a preferred embodiment, the portion of the air flow is directed through at least one of the plurality of flow channels.
In a preferred embodiment, each of the plurality of flow channels has a major longitudinal axis and wherein the major longitudinal axis of each of the plurality of flow channels is generally parallel to the major longitudinal axis of the ionization head.
In a preferred embodiment, the ionization head comprises a multi-point ionization head.
In a preferred embodiment, the present invention further comprises a fan arranged for operative use with the air flow channel for moving the air in the upstream to downstream direction through the air flow channel.
In another embodiment, the present invention provides a filtration system for filtering particulates from air flowing in an upstream to downstream direction in an air flow channel. A point ionization source is oriented to generate ions in the proximity of the air flow channel, the ions predominately having an electrical charge with respect to ground. A particulate collection surface is positioned within the air flow channel in a downstream direction from the point ionization source, the particulate collection surface being electrostatically charged in an opposite direction with respect to ground than the electrical charge of the ions. A portion of the air flow is directed.
In a preferred embodiment, the portion of the air flow directed past the ionization source in a direction generally opposite to the upstream to downstream direction is air flow which is downstream of the particulate collection surface.
In an alternative embodiment using an axial fan, a filtration system filters particulates from air flowing in an upstream to downstream direction in an air flow channel. A point ionization source, if used, is oriented to generate ions in the proximity of the air flow channel, the ions predominately having an electrical charge with respect to ground. A channel filter particulate collection surface is positioned within the air flow channel in a downstream direction from the optional point ionization source and electrostatically charged in an opposite direction with respect to ground than the electrical charge of the ions. An axial fan is arranged for operative use with the air flow channel for moving the air in the upstream to downstream direction through the air flow channel.
In a preferred embodiment, the axial fan is positioned within the air flow channel.